1. Field of the Invention
The present invention relates to a liquid discharge device and, in particular, to a liquid discharge device suitable for printing heads that are used to recording apparatus of the following: various printers, recorders, facsimiles, or printers used for formation of patterns in the fields of textile printing and ceramic industry, or pumps that are used to precisely discharge and transfer liquid such as adhesive or ink, wherein characters and images are printed by discharging a drop of ink from a fine liquid outlet orifice.
2. Description of Related Art
Piezoelectric ceramics have been used in, for example, piezoelectric actuator, filter, piezoelectric resonator (including oscillator), ultrasonic oscillator, ultrasonic motor, piezoelectric sensor and pressure pump. Among these devices, the piezoelectric actuator is applied as the piezoelectric actuator for positioning an X-Y stage of semiconductor manufacturing equipment or as the piezoelectric actuator for liquid discharge device (printing head) of inkjet recording apparatus, by taking advantage of the very high response rate to electrical signals, in the order of 10−6 seconds.
As for liquid discharge device mounted to this ink-jet recording apparatus, the following systems are generally known: (1) Thermal head system, wherein a heater is prepared as a compressing tool within a liquid compressing chamber filled up with ink, and the heater heats and boils the ink so that bubbles can be generated within the liquid compressing chamber to compress the ink to discharge a drop of ink from a liquid outlet orifice; and (2) Piezoelectric system, wherein a certain portion of wall of a liquid flow passage with ink filled is bent and displaced by piezoelectric displacement elements of a piezoelectric actuator to mechanically compress the ink in a liquid compressing chamber, thereby discharging a drop of ink from a liquid outlet orifice.
Among these, the liquid discharge device that employs piezoelectric system is composed of a piezoelectric actuator wherein a plurality of piezoelectric displacement elements are formed and a flow passage member that has liquid inlet orifices, liquid compressing chambers and liquid outlet orifices. The piezoelectric actuator is placed on the flow passage member, so that the piezoelectric displacement elements correspond in position to the liquid compressing chambers. A plurality of piezoelectric displacement elements are formed from a piezoelectric ceramic layer that consists of perovskite piezoelectric ceramics containing Pb such as lead zirconate titanate (PZT), and electrodes that are disposed on the both sides of the piezoelectric ceramic layer. When driving voltage is applied from the both sides of the piezoelectric displacement elements, the piezoelectric displacement elements are displaced to discharge a fine drop of ink from the liquid outlet orifices (For example, Japanese Patent Application Laid-Open No. 11-34321).
Japanese Patent Application Laid-Open No. 2003-154646 proposes an ink-jet head wherein liquid compressing chambers are disposed in 4 to 10 lines, and dot density in sub-scanning direction is not less than 300 dpi (dots/inch) for one pass scanning of a head in main-scanning direction. This ink-jet head can contribute to miniaturization of ink-jet heads and higher dot density.
However, in the liquid discharge device according to Japanese Patent Application Laid-Open No. 2003-154646, since wiring (extraction electrodes) for applying driving voltage is passed between the neighboring piezoelectric displacement elements, when the piezoelectric displacement elements are too close, there is a risk that the piezoelectric displacement elements will touch the extraction electrodes, thus causing poor conduction. Further, when the neighboring piezoelectric displacement elements are too close, displacement of one piezoelectric displacement element induces another displacement of its neighboring piezoelectric displacement element, which influences discharge speed of ink drops, resulting in poor image quality. That means there is a problem that so-called cross talk has large influence.
Moreover, in the liquid discharge device according to Japanese Patent Application Laid-Open No. 2003-154646, when dot density is much higher (for example, from 300 dpi to 600 dpi), the area of driving portion in the piezoelectric displacement elements is made smaller to create spaces between the neighboring piezoelectric displacement elements, and the extraction electrodes in the neighboring lines are placed in these spaces. However, when the area of the driving portion is too smaller, displacement of the piezoelectric displacement elements is also smaller, and discharge speed of ink drops is lowered by cross talk influence, causing less accuracy of ink landing and poor image quality. Thus, higher dot density has limitation. Further, in order not to lower ink discharge speed, driving voltage needs to be high, which leads to an increase in power consumption.